1. Field of the Invention
This invention relates to a control and power device for a rotary electrical machine, comprising a control circuit and a power circuit, the power circuit including a plurality of power transistors and control circuits associated with the transistors. The invention finds applications in the field of the automotive industry, and in particular in the field of alternators and alternator starters.
2. Description of the Related Art
In a motor vehicle having a heat engine and an alternator, both included in one casing, the alternator comprising the following:
a rotor, which represents an inductor or inductance, which is conventionally associated with two slip rings, and two brushes by which an excitation current is applied; and
a multi-phase stator carrying a plurality of coils or windings, representing an armature, which are either star connected or delta connected in the most frequent case of a three-phase structure, and which deliver electric power to a rectifier bridge when the machine is working as an alternator
The stator surrounds the rotor, the brushes of which are connected to a regulator of the alternator in order to maintain the voltage of the alternator at a desired voltage between 12 and 14V for a battery, according to whether the latter is flat or charged, respectively.
The alternator enables rotational motion of the inductive rotor, driven by the heat engine of the vehicle, to be converted into an armature electric current which is induced in the windings of the stator.
The alternator is also able to be reversible and to constitute an electric motor, enabling the heat engine of the vehicle to be driven in rotation via the rotor shaft. This reversible alternator is also called an alternator starter or a starter alternator. It converts mechanical energy into electrical energy and vice versa.
Accordingly, in the alternator mode, the alternator starter, in particular, charges up the battery of the vehicle, while in its starter mode the alternator starter drives the heat engine, also referred to as an internal combustion engine, of the motor vehicle in order to start it.
A power unit is provided which is connected to the phases of the stator and which is connected between earth and a power supply terminal of a battery. The power unit serves as a control bridge or wave generator of the phases when the alternator starter is working in starter mode and serves as a rectifier bridge when it is working in alternator mode. For example, it comprises diodes which are associated with transistors of the MOSFET type, which are well known to the person skilled in this field, and is controlled by a control unit.
At the present time it is conventional to provide a power unit in which the power transistors constitute a bridge of interrupters, and are controlled in synchronism with the current which is present in one winding of the stator, and this is called synchronous rectification.
It is thus necessary to control the transistors by means of a relatively sophisticated control unit, such as for example a micro-controller, current sensors for detecting the direction of the current in the windings of the armature of the alternator, etc.
In a first known embodiment, the power unit, comprising the rectifier bridge and the control unit, constitutes an electronic control and power module which is most commonly fitted on the outside of the alternator starter with which it is connected through electrical wires that are connected to the output terminals of the phases of the stator.
In a second embodiment, which is described in European patent EP-A1-0911958, it is arranged that the electronic control and power module is placed directly in the casing of the alternator starter, which avoids the above mentioned electrical wires and thereby avoids problems of fitting on the vehicle. For this purpose, the control and power module is miniaturized.
However, because of the increasingly severe restrictions of miniaturization, and manufacturing constraints, in particular as regards the dimensions of the casing that have to be followed, the size of the electronic control and power module is a problem due to the numerous components which are necessary in the module, and due also to the interconnections by which these various components are connected together.